The present invention relates generally to separable blade agitators and more particularly to a glass coated agitator and the apparatus and method for assembling the agitator within a mixing vessel.
Separable blade agitators are well known in the art and are described for example in U.S. Pat. Nos. 2,811,339 and 3,494,708. Briefly, a separable blade agitator includes a drive shaft and a separable impeller. The impeller includes a hub for attachment to the drive shaft and two or more blades extending outwardly from the hub. The entire surface of the drive shaft, hub and blades exposed to the contents of the vessel is glass coated to resist corrosion, adherence and abrasion. Such separable blade agitators are used in vessels for mixing various corrosive, adhesive, abrasive or easily contaminated ingredients such as acids, polymers, pharmaceuticals, dyes and the like.
These agitators especially have great value in closed vessels because they eliminate the need for large vessel openings normally used for agitator removal and admittance. In this respect, the separable impeller portions can be passed into a pressure vessel through a relatively small manhole opening and assembled within the vessel to the drive shaft.
Separable blade agitators are useful in either closed or open vessels in that they permit replacement of damaged impellers or changing the size or type of impeller without the need to remove the entire agitator (i.e. drive shaft and impeller) from the vessel or to disconnect the drive shaft from the drive motor and seals.
Separable blade agitators having gaskets between the shaft and impeller are known. Such agitators are not entirely satisfactory because any gasket used must be made from tantalum or other exotic metal or from a fluro-carbon in order to resist the highly corrosive environments to which these gaskets may be exposed. Another drawback with gaskets is that they take a set due to repeated heating and cooling and eventually leak. Normally, leaking gaskets can be resealed by tightening, but this is difficult to do in separable blade agitators and often a leak is not noticed until leakage into the shaft has caused damage.
Separable blade agitators are also known in which no gaskets are used, as shown for example in U.S. Pat. No. 3,494,708. Here a gasketless connection is made by forcing near optically flat glass coated surfaces together with considerable force. The primary drawback of the construction shown in this prior art is that relatively complicated, expensive components, which themselves are not glass coated, are needed to hold the shaft and agitator portion together in a fluid tight gasketless connection capable of transmitting torque from the drive shaft to the impeller blades.
Thus, prior art separable blade agitators used gaskets or optically flat surfaces between joints to seal the joints between the separable members and isolate non-corrosive resistant surfaces from the vessel contents. The present invention, however, does not rely on sealed joints because all surfaces exposed to the vessel contents are protected by non-corrosive coatings such as glass or plastic.
In the present invention, the configuration of both the drive shaft and separable impellers is such that they can be quickly and easily joined in an interference fitted, gasketless connection. The invention not only provides a safe connection because all exposed surfaces are glass coated, but also provides for relatively high torque transmission because of the cross sectional configuration of the hub of the impeller and a port on of the shaft to which the hub is attached.